He also noted that he would be sending a letter to the Judiciary Committee to "explain this comment for the record."

But Blumenthal argued that a written letter isn't sufficient because "it is not under oath. It is not subject to questioning."

"[And] If it not a credible explanation, he will have to resign," Blumenthal said.

The Washington Post reported Wednesday evening that Sessions spoke to Russian Ambassador Sergey Kislyak during the presidential campaign, then denied having contact with Russian officials under oath during his confirmation hearing.

Durbin added on Thursday that Sessions's decision to recuse himself is "essential" but that he also believed Sessions needed to testify under oath about the matter.

Democrats, in the minority on both the committee and in the Senate, hold limited sway to get Sessions to reappear or force an independent commission to look into any talks between the Trump campaign and Russia.

The Iowa Republican added he was glad Sessions was sending the committee a letter but didn't signal that he would recall the former GOP senator to testify.

"I appreciate that he will be sending a letter to the committee, as I asked him to do, to clear up any confusion regarding his testimony so we can put this issue to bed once and for all," Grassley said.